If the price that has been reported is accurate, every square foot of the piece of fibreboard that was sold in New York this week cost more than $4m (£2.1m). But then it was covered in an intricate web of lines in reds, yellows, blues and greys, splashed on to it by a man called Jackson Pollock.

The $140m quoted as the price obtained by Sotheby's for Pollock's Number 5, 1948 would make it the highest figure known to have ever been paid for a painting. It would break the record believed to have been set in June when Gustav Klimt's gold-flecked portrait of Adele Bloch-Bauer from 1907 was bought by the cosmetics magnate Ronald Lauder for a reputed $135m. The prices all have to be heavily qualified because sales of fine art masters between private owners are among the most tightly controlled and secretive deals around. Even the $135m fetched by the Klimt has yet to be officially confirmed.

A spokesman for Sotheby's would only say that "the parts of Sotheby's that are public are the big auction sales. Even if [the Pollock sale] had happened it was not at auction and no information is available".

The story of the Pollock sale was broken in yesterday's New York Times, which reported that the painting had been put up for purchase by its current owner, David Geffen. Ranked number 45 in the Forbes list of richest Americans, with a net worth of $4.5bn, Geffen was one of the three founders along with Steven Spielberg of the Dreamworks movie studios. He is a keen collector of American artists' work, including Pollock, Mark Rothko and Willem de Kooning. Last month he sold two other paintings by Jasper Johns and de Kooning for a combined sum of $143.5m, prompting speculation that he was storing up resources for a bid to buy the Los Angeles Times newspaper.

The buyer of the Pollock, according to the sources quoted anonymously by the New York Times, was a Mexican financier who is also shrouded in secrecy, David Martinez. Little is known about him other than that he has recently embarked on a blitz of fine art purchasing. He bought a de Kooning at the Basel art fair in June for $15.5m. He is also known to have spent $55m buying his apartment at Columbus Circle in Manhattan.

Swaying

The Pollock work, Number 5, 1948, is 1.2 by 2.4 metres (4 ft by 8ft), and is one of his first drip paintings. He had begun to experiment with the technique the previous year, placing the surfaces of the paintings on the floor and manipulating colours on to them by swaying and swinging his body above them.

In the confined space of his East Hamptons studio in Long Island, Pollock used the drip painting method as a way of touching base with his subconscious in the spirit of what became known as abstract expressionism. In 1956 Time Magazine dubbed him Jack the Dripper - a name that has stuck at a popular level but which art experts disdain as vulgar.

By 1948 the artist had begun to compose works that dispensed entirely with the brush and relied completely on pouring the enamel paints on to the surface. He used a variety of backgrounds, from canvas to paper with a gesso primer to this work's engineered wood surface known as fibreboard.

"1948 was his miracle year. It was the year in which he really got into his stride with drip painting," said Jeremy Lewison, the former director of collections at the Tate who has written a book on Pollock and is now an art consultant.

In Mr Lewison's reckoning, the painting stands alongside the other great works Pollock produced that year, Summertime, Number 9A, in the Tate collection; Number 1A, 1948, in New York's Museum of Modern Art; and Number 26A, 1948, held at the Pompidou centre in Paris.

Pollock commands such huge prices partly because of his stature as the American artist par excellence, and because in the immediate post-second world war years he broke the mould set by European artists. "Jackson broke the ice," de Kooning said about him.

Astronomical amounts are also more likely to change hands because it is so rare that masterpieces held in private ownership come on to the market, most already being owned by the major museums. And a third factor is that the art market is awash with cash, with new money flooding in from Russia, the Far East and Latin America and pushing prices dramatically upwards.

November is traditionally a time for the big money sales in New York's auction houses. Sotheby's and Christie's will be putting up for sale several masterpieces by impressionists, modernists and current artists. Their catalogues include names such as Cezanne, Picasso, Gauguin and Andy Warhol.

Next week four Klimts will go on sale at Christie's, valued collectively at $100m. The paintings, along with the then record-breaking Klimt sold in June, have all come on to the market as a result of a lengthy legal action which forced the Austrian government to release the paintings to a niece of Adele Block-Bauer who lives in Los Angeles.

Jack the dripper

Pollock was born in Cody, Wyoming, in 1912 and grew up in Arizona and California, attending Los Angeles' Manual Arts High School. He later moved to New York City, and studied under Thomas Hart Benton at the Art Students' League.

His early work was influenced by the Mexican muralists Siqueiros, Orozco and Diego Rivera. After visiting exhibitions of Picasso and surrealist art, his work became increasingly symbolic.

In 1944 Pollock married his lover Lee Krasner and in 1945 they moved to Springs in East Hampton, on Long Island, New York.

To cope with depression he became interested in psychotherapy and in Carl Jung's theory of primitive archetypes, which formed the basis of his work between 1938 and 1944.

After 1951 his work became darker in colour, often only black. He had moved to a more commercial gallery and there was great demand from collectors, contributing to his alcoholism.

He died in a car crash in Springs on August 11 1956, aged 44.

His painting Blue Poles was sold to the National Gallery of Australia in 1973 for $2m - then the highest price ever for a contemporary work.